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Mosquito Control Basics

WHY DO WE NEED TO CONTROL MOSQUITOES?

There are really only two reasons to control mosquitoes; to avoid nuisance biting, and to preclude the spread of mosquito-borne disease. Everyone recognizes that mosquitoes can be a real nuisance, but most people do not realize the magnitude of the health threat that they represent. Some of the world's most dreaded diseases are known to be carried and transmitted by mosquitoes. Many countries around the world are ravaged yearly by malaria, yellow fever, and dengue-hemorrhagic fever. In the United States, encephalitis and dog heartworm are the primary mosquito-borne diseases, but dengue has recently crossed the Mexican border into Texas and is now seen as a serious public health threat.

Mosquito-borne encephalitis in the U. S. is prevalent in several forms and is geographically wide-spread. In Colorado, the Western Equine and St. Louis viral strains were the most common before the invasion of West Nile Virus in 2002. West Nile Virus entered the US along the east cost in 1999 and has had serious implications for the rest of North America. (Please see our West Nile Virus Page for more detailed information). Encephalitis is an inflammation of the brain and central nervous system, and is characterized by a high to moderate mortality rate, with some survivors left with permanent physical and mental disabilities.

A growing threat to Colorado pet owners is dog heartworm. A parasite transmitted by the mosquito becomes lodged in the heart and lungs, and if left untreated, severe physical damage and death may occur. Beyond viral and parasitic diseases, other health problems caused by mosquitoes include allergy and infection. In some cases, the chemicals within the mosquitoes saliva are injected into its blood-meal victim, causing serious allergic reactions.

Health concerns are certainly not the only reason to control mosquitoes. If you've ever been driven inside by mosquitoes during a backyard picnic, or had to cancel an important outdoor event because of mosquito annoyance, or have chased one pesky invader around the bedroom in the middle of the night, you know the value of effective mosquito control. Mosquitoes can be annoying enough to make an area uninhabitable or unsuitable for recreational or industrial development. Economic losses can also be considerable in resort areas and at local tourist attractions.

PUBLIC EDUCATION

Educating the public about mosquitoes and how to control them is the first place to start when trying to reduce mosquito populations. In many cases, residents, once they know where to look can identify and eliminate potential mosquito breeding habitat around their homes and neighborhood.

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THE BENEFITS AND THE RISKS

As with most things in life, benefits do not usually come without some associated risks. Mosquito control is no different. Complete mosquito eradication is impossible, thus man's effort to control mosquitoes is an on-going battle. In the previous sections, we have discussed the benefits to be derived from controlling mosquitoes. Those being, a greatly reduced threat from mosquito-borne disease, and an overall improvement in the quality of life. On the other hand, the risks associated with mosquito control also concern human health, and the health of our natural environment. In the following sections we will discuss these risks, and how, through modern technology, mosquito control agencies have been able to reduce the threat to human health and the environment.

INTEGRATED MOSQUITO MANAGEMENT

"A process consisting of the balanced use of cultural, biological, and least-toxic chemical procedures that are environmentally compatible and economically feasible to reduce pest and disease-vector populations to a tolerable level"

The goal of Colorado Mosquito Control and all other mosquito control agencies must be;

"To control mosquitoes in a safe, efficient, and economic manner while preventing damage to humans, wildlife and the natural environment"

This task is accomplished is through the implementation of a comprehensive plan of integrated control approaches, know as Integrated Mosquito Management (IMM). The plan is based on sound scientific knowledge and makes use of the latest technology, equipment and materials. When brought together these methods furnish a cost-effective level of mosquito suppression needed to protect man and domestic animals from harassment and the disease. This concept means more than simply combining several technological approaches.

To successfully control mosquitoes, we must know:

1. Which mosquito species are locally important as the primary
source of intolerable annoyance or as vectors of disease.

2. Where the breeding sites of these mosquito species are located.

3. When the mosquitoes are developing in these breeding sites and
when the emergence of adult mosquitoes will take place.

4. What mosquito control measures are needed and can be applied
effectively, economically, and safely with minimal disruption to the
local environment.

5. How much funding will be required to coordinate and execute the
plan devised. Thus, a modern integrated mosquito management
program requires a vast array of knowledge and competence in a
number of technological specialties.

Integrated Mosquito Management (IMM) Operations at CMC

IMM at CMC means that approximately 94% of our time, labor and pesticide expenses are targeted toward finding and controlling mosquito larvae with biological controls in a bio-rational, environmentally sound manner.

LARVAL AND PUPAL SURVEYS

The basis of every CMC mosquito control program is a comprehensive survey. The survey is used to locate and map all potential larval development habitats, to identify the mosquito species present, and to predict the time and location of effective control strategies. Survey methods include; wetlands inventories, larval and pupal surveys, and adult mosquito monitoring. Larval and pupal surveys are very effective and efficient in monitoring populations and species content. But before routine breeding site inspection and larviciding operations can begin, all sites within the proposed jurisdiction must be identified and mapped. The potential mosquito breeding sites can be identified using new digital GIS technology, USGS maps which are available for most areas digitally, digital aerial photos and satellite imagery.

ADULT MOSQUITO MONITORING

Several methods are available for sampling adult mosquitoes. CDC light traps are the most common and are used in most Colorado Mosquito Control, Inc. control programs. The traps are used to capture nocturnal mosquitoes that are CO2 and light attractive. A CDC trap consists of a canister which emits CO2 , a small incandescent bulb to attract the mosquitoes, and a fan to force them down into a mesh net. The adult mosquitoes are then sorted to sex and species and counted, with the results entered into the computer for trend analysis. Season-long trapping results can be used to identify population trends, component species and to effectively time spray applications. Other techniques include sweep netting vegetation and taking landing/biting counts.

COMPUTER TECHNOLOGY & MOSQUITO CONTROL

Today one of the most important tools in our arsenal against mosquitoes is not a new spray machine or some high tech insecticide, but a computer. Computer technology, as in most industries, has become an intricate part of a modern mosquito control operation. CMC's computers are used in variety of ways including a Geographic Information System (GIS) which is used to store, breeding site inspection results, land owner information, mosquito population data, local weather data and to develop comprehensive maps used operationally and to report control results to our clients. Complex spatial analysis can also be performed to recognized relationships between mosquito breeding sites and human annoyance or disease transmission.

Historical site profiles are developed for individual breeding sites, allowing CMC to generate site inspection plans targeted to historically active sites precisely when breeding is occurring. CDC trapping results are also stored in a database, and the results can be graphically monitored so that even minute population changes can be recognized and dealt with. Computer models are also being developed to help understand the complex biological and environmental factors involved in the transmission of mosquito-borne diseases such as Western Equine Encephalitis. Colorado Mosquito Control, Inc. is dedicated to using the latest state-of-the-art technologies to give our customers the best and most cost-effective mosquito control programs available.

BIOLOGICAL AND PHYSICAL CONTROL OF MOSQUITO LARVAE

The primary objective of the Integrated Mosquito Management program is to inhibit the development of mosquito larvae so as to minimize the need for "fogging" with chemical insecticides to control adult mosquitoes. The use of ULV (ultra-low volume) formulated insecticides for use in ground application truck or ATV-mounted equipment gives only temporary relief and is not very cost-effective and although adult mosquito suppression by ULV fogging is desired by some citizens, it can be strongly opposed by others.

Biological control methods take advantage of natural enemies to reduce mosquito populations. These natural enemies can fall into one of three categories; they prey on mosquitoes, parasitize them, or act against their hormonal systems to preclude complete development. CMC uses biological controls in all three categories.

Mosquitofish, Gambusia affinis, or the Colorado native plains killifish Fundulus zebrinus, are small surface feeding minnows which readily attack and devour aquatic stage mosquitoes. These mosquito eating fish are stocked seasonally in semi-permanent and permanent water sites known to produce mosquitoes. They are very adaptable to most water conditions, bear live young which begin feeding immediately, and their gestation period is quite short so that they are able to produce several generations per season. Plus, one full grown adult can devour over 100 mosquito larvae per day.

Bti (Bacillus thuringiensis sub. israeliensis)

Bti is an environmentally responsible bio-larvicide derived from Bacillus thuringiensis sub. israeliensis (Bti), a naturally occurring spore and crystal forming soil bacterium. The active ingredient of Bti is a crystalline delta-endotoxin. Mosquito larvae are killed through the ingestion of the delta-endotoxin. When larvae ingest the Bti, the delta-endotoxin reacts with the stomach secretions and causes gut paralysis and death. Bti is the most widely used mosquito larvicide in the United States. The safety of Bti was determined by extensive toxicological testing before approval for use. Research and field trials have shown that Bti has no toxic effects on beneficial and predacious arthropods and insects such as honeybees, beetles, mayflies, dragonflies, damselflies, stoneflies, caddisflies and true bugs. Among Diptera (true flies and midges) Chaoborus species, Ephydra riparia, Musca domestica, Odontomyia species, and Polypedilum species showed no susceptibility to Bti. Varying degrees of mortality occurred among Chrironomus pulmosus, Chrionomus stigmaterus, Dixa species, Goeldchironomus holoprasinus and Palpomyia species. Among butterflies and moths, low levels of toxicity were observed only in Aporia crataegi, Euproctis chuysorriea, and Malacosoma neustrium. No toxicity from Bti was observed in crustacea including larvivorus copepod species, fish, oysters, shrimp, crabs, mollusks, flatworms, and amphibia.

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Bacillus sphaericus

Bacillus sphaericus, like Bti is also a naturally occurring soil bacteria with mosquito larvicidal properties. Additionally Bsph has the favorable property of a longer persistence in nature and the ability to release fresh spores into the water column and to recycle itself. This recycling offers an extended residual control of newly hatched mosquito larvae. Bsph contains toxic protein crystals and living spores which larvae feed upon. In the larvae's gut, enzymes dissolve the crystals in to smaller crystals called protoxins. The protoxins almost immediately begin to paralyze the gut and within a few hours break through pores in the gut wall and invade the body cavity where they begin to multiply. The mosquito larvae will die within two days.

Altosid (methoprene)

Another biological control material used by CMC is Altosid® (methoprene), which is a hormonal insect growth regulator (IGR). Altosid briquets, pellets, granular and liquid can be used in environmentally sensitive areas because they do not kill the larvae, but only stop complete metamorphosis, thus allowing the larvae to remain within the food chain. Methoprene disrupts normal mosquito development and metamorphosis, preventing the emergence of breeding, biting adult mosquitoes.

SOURCE REDUCTION

Physical mosquito control usually involves manipulation of the natural environment (usually wetlands) to disrupt larval mosquito development. This can include dredging, ditching and the raising or lowering of water levels. Due to today's strong emphasis on protection of wetlands, source reduction is not usually a feasible option for controlling mosquitoes. Other than clearing clogged existing ditches, CMC does not use any of the common physical control measures such as ditching or wetland drainage in its programs.

CHEMICAL MOSQUITO CONTROL

Aside from source reduction, using pesticides to reduce mosquito populations is the oldest form of control. Chemical mosquito control has the considerable advantage of succeeding where the physical and biological methods are infeasible, uneconomical or only partially successful. Chemical insecticides will usually give immediate control of either larvae or adult mosquitoes. Several insecticide formulations and application options exist in modern mosquito control, but each have their drawbacks. In the long run chemical insecticides can be expensive, may cause environmental damage and are only a temporary means of control.

MOSQUITO LARVICIDING

Mosquito larval habitats are identified and mapped early in the program's development. An ongoing seasonal program of site inspection and subsequent larviciding, when the sites are determined to contain larvae, is the key to effective larval control. CMC generally uses only five larval control agents in its programs; the biologicals; Bti, Bsph, Altosid® IGR, and mosquitofish as discussed above, and Abate® (temephos) a low toxicity organophosphate insecticide which is used only on a limited site specific and/or emergency basis. All materials and application methods used are regulated by the U.S. EPA and Colorado Department of Agriculture.

ADULT MOSQUITO CONTROL

Mosquito control activities are limited to specific political boundaries, and biological larval control efforts are therefore limited to certain areas. Adult mosquitoes however, can migrate long distances and do not obey lines on a map. Thus any mosquito control program that hopes to effectively control mosquitoes must contend not only with local larval development, but also with invading adult mosquitoes from outside the program's jurisdiction or from inaccessible areas within the programs boundaries.

The adult mosquito management portion of the Integrated Mosquito Management Program consists of two phases: Harborage Site Adulticiding and General Adulticiding. The goal here is to concentrate control efforts in adult mosquito harborage areas with high humidity gradients such as stream or river valleys, margins of thick woodlots, and densely vegetated parks and recreational areas, away from the human population.

The dispersal of adult mosquitoes into residential areas can be reduced or slowed by applying adulticide materials into the harborage areas where adult mosquitoes congregate. As a result, general adulticiding can be limited to periods of excessively high annoyance, or during a public health emergency. Nature has provided no successful alternatives to the use of chemical insecticides to control adult mosquito populations. The controlled and targeted application of chemical insecticides is the only currently available alternative.

Through the use of modern technology, equipment and insecticides, effective control of adult mosquitoes by ultra-low volume (ULV) spray application is possible. ULV is the key to this technology, whereby an extremely small amount of insecticide can be applied over a very large area, (in the case of Biomist 3+15®, 1.0 ounce per acre) thus controlling adult mosquitoes while not adversely affecting man, wildlife, or the environment. With accurate timing and precise application, a kill rate of over 90% of the adult mosquito population within the target area can be achieved.

A truck or ATV-mounted ULV spray machine is used to produced very small (<20 micron diameter) droplets of the insecticide, and to disperse this insecticide downwind to the target area. The application is timed so that it coincides with the peak of mosquito annoyance after a hatch, and with the daily period of greatest activity, through the evening and early morning hours.

AquaLuer®, Biomist 3+15® , Permanone® and Anvil 2+2®, are permethrin and sumithrin products, respectively, they are man-made versions of the natural botanical insecticide, pyrethrin. They offer excellent effectiveness against adult mosquitoes, low mammalian toxicity, low odor and rapid bio-degradability. AquaLuer® , Biomist® and Anvil® are the "least toxic" products registered with the EPA for ULV adult mosquito control and are the primary adulticide used in CMC contracted communities.

All materials have been chosen for their excellent long-term safety record, and their effectiveness in the field. Each material has a specific set of conditions under which it will be used, namely, label specifications, mosquito population size and species make-up , expected temperature range, and community acceptance.